Primordial Stars
For a classification of stars see The H-R Diagram. The first stellar population, known as Generation III Stars, were completely different from the stars that exist today. They were more massive then all the stars that exist today. No telescope was able to image them, so their existence is mostly theoretical. These stars are long extinct. However, in the multiverse theory, there might be an universe that is much younger then ours and such stars could exist right now. Also, a few less popular theories suggest that somewhere in our Universe, matter is still being created or that in some parts time is flowing very slowly. Even if population III stars no longer exist anywhere, it still is possible that an advanced civilization will be able to build a time machine and try to explore them. Formation Before the formation of the first stars, the Universe was composed of large nebulae of hydrogen gas, with traces of helium. Some suggest that traces of lithium also existed. Gravity started to compress clouds of gas, making them to heat-up to a point of stability. This process can be seen today and it is the cause of star formation. The main difference is that hydrogen and helium, below 200 K, don't cool by releasing a significant number of infrared photons. Today, thermal energy is transferred to heavier elements, which cool faster by radiating infrared light. The heat resulted prevents the cloud from collapsing, opposing gravity. The minimum mass for a cloud to collapse, known as Jeans mass, is much higher when you have a heated gas. Unfortunately, we don't know exactly how much hydrogen, how much helium and how much lithium existed at that time. If we could know, we could estimate how much infrared light could be produced to cool down the clouds. There are various estimations. A round estimation for the Jeans mass is 400 Solar masses. Today, no known star is that massive. However, this is the lower limit. The upper limit is unknown. In our epoch, massive clouds will simply collapse into smaller ones, creating many stars. In the early Universe, stars far more massive then 1000 Solar masses could be formed. Characteristics Population III stars were more massive then any star that exists now. They were blue, very bright and with surface temperature around 100 000 K. The closest relatives today are O - type stars. Being so bright, they certainly had a very powerful Stellar Wind. Particles in the wind were strongly accelerated by the powerful light. Also, their light was not much into visible spectra. They had a strong ionizing UV and X radiation, which certainly affected the environment around, compressing other hydrogen clouds and forcing other stars to be born. Since at that time there was nothing heavier, planets could not form. So, terraforming anything is out of question. There was no solid surface and there were no heavier elements. Explosions Such massive stars are short lived. They could not sustain energy production for more then a few millions of years. As they exhaust hydrogen, they don't have enough time to further evolve. Heavier elements are fused extremely fast. Classic Supernova. Many of the primordial stars exploded in powerful supernovas, creating the first heavy elements in the Universe. Given their mass, the explosions must have been incredibly powerful and could be responsible for creating heavier elements all the way to uranium. Pair Instability Supernova. Currently, stars with low metalicity and with a mass varying between 130 and 250 Solar masses can explode in a pair instability supernova. The principle is as follows: When the star is trying to fuse oxygen, pressure and temperature in the core reach a critical value, when pairs of particles and antiparticles (for example electrons and positrons) are created. This leads to a temporary loss of energy, forcing the star to contract, to produce more nuclear energy. However, as particles and antiparticles annihilate each other, a tremendous amount of energy is released, causing a runaway nuclear reaction. The star is ripped apart and explodes, without letting anything behind. During pair instability supernovas, large amounts of heavy elements are produced. However, primordial stars were larger then what is required for a pair instability supernova. Some authors argue that for much larger stars, over 10000 Solar masses, the same process would occur when the star tries to fuse helium into oxygen. Such stars will produce the most massive supernovas of all times. Quasi-Stars. For a star that weights between 1000 and 10000 Solar masses, another scenario is possible. They are called quasi-stars. When the core exhausts its fuel, it collapses into a black hole. Because the star is too large, the shock wave cannot travel all the way to the surface and no supernova is visible. Instead, the black hole remains inside the center. As matter falls into the black hole, it produces far more energy then it could produce through nuclear fusion. The star increases in size, reaching about 60 AU in diameter. Quasi-stars were the largest stars of all times. Placed inside the Solar System, such a star would extend all the way to Neptune or even further. They were orange-colored, with a surface temperature of 4000 - 5000 K and with extremely powerful solar winds. Their lifetime is expected to be around 7 million years. After the star is completely devoured, an intermediate-size black whole is left in its place. Options for life and settlers Unfortunately, primordial stars had no planets around them. At first, there were no heavier elements. It is possible that, at some point, heavier elements started to form in large enough amounts, but still, population III stars continued to rule the cosmos. Even so, since these stars lived so little, a planet had no time to get formed. With their powerful solar winds, a protoplanetary disk would had been pushed into interstellar environment very fast. With only hydrogen and helium around, we could suspect that the first planets formed were gas giants. Still, it is possible that, at some point, from the debris left after a supernova, a rocky planet could have formed. At that time, light was more into the UV and X spectra, gas was strongly ionized and supernovas lurked the sky so often. That planet was not a good place for life, but it is the only solid surface that a space traveler might find. Category:Stars and other hosting celestial bodies